Combinaison crédibiliste de classifieurs binaires

The problem of binary classifier combination is adressed in this article. This approach consists in solving a multi-class classification problem by combining the solutions of binary sub-problems. We consider two strategies in which each class is opposed to each other, or to all others. The combination is considered from the point of view of the theory of evidence. The classifier outputs are interpreted either as conditional belief functions, or as belief functions expressed in a coarser frame. They are combined by computing a belief function that is consistent with the available information. The performances of the methods are compared with those of other techniques and illustrated on various datasets.Nous étudions dans cet article le problème de la combinaison de classifieurs binaires. Cette approche consiste à résoudre un problème de discrimination multi-classes, en combinant les solutions de sous-problèmes binaires ; nous nous intéressons aux stratégies opposant chaque classe à chaque autre, et chaque classe à toutes les autres. La combinaison est considérée ici du point de vue de la théorie de Dempster-Shafer : les sorties des classifieurs sont ainsi interprétées comme des fonctions de croyance, conditionnelles ou exprimées dans un cadre plus grossier que le cadre initial. Elles sont combinées en calculant une fonction de croyance consistante avec les informations disponibles. Les performances des deux approches sont comparées à celles d’autres méthodes et illustrées sur divers jeux de données

Postal decision fusion based on the Transferable Belief Model

In order to improve decision-making in automatic recognition of postal addresses, a model for the fusion of postal address recognition systems (or OCR engine, for optical character recognition) based on belief functions theory is exposed. This theoretical framework offers a great flexibility in the representation and combination of the decisions provided by the OCRs, each one being able to provide a complete or a partial postal address. In this article, we describe the chosen frame of discernment, the mass assignment developped from a hierarchical organization of the decisions and the decision-making method. Experimental results show a real improvement of the LAPs’ individual performances.Afin d’améliorer la prise de décision pour la reconnaissance automatique d’adresses postales, un modèle de fusion de décisions de lecteurs d’adresses postales (LAP) basé sur la théorie des fonctions de croyance est exposé. Ce cadre théorique offre une grande flexibilité dans la représentation et la combinaison des décisions fournies par les LAP, chacun pouvant fournir une adresse postale complète ou partielle. Dans cet article, nous détaillons le cadre de discernement choisi, l’affectation des masses basée sur une organisation hiérarchique des décisions, et la méthode de prise de décision adoptée. Les résultats obtenus montrent une réelle amélioration par rapport aux performances individuelles des LAP

Variabilité des régimes pluviométriques et hydrologiques en cette fin de siècle en Afrique de l'Ouest et Centrale non sahélienne

L'étude présentée s'appuie sur des mesures de précipitation et d'écoulement enregistrées dans les régions non sahéliennes d'Afrique de l'Ouest et Centrale (du Sénégal à la Centrafrique) au cours du XXème siècle . Elle repose sur un ensemble de méthodes d'interpolation et de représentation cartographique, ainsi que sur des méthodes statistiques de détection de ruptures au sein des séries chronologiques. Les séries pluviométriques annuelles enregistrées sur de longues durées ont permis d'étudier l'évolution spatio-temporelle de la pluviométrie dans ces régions. Les résultats soulignent l'existence d'une alternance de périodes sèches et humides depuis le début du XXème siècle. Ils mettent également en évidence une diminution nette de la pluviométrie dans ces régions d'Afrique, dites humides, depuis la fin des années 1960 et le début des années 1970.La sécheresse actuelle ne semble pas avoir connu d'équivalent, ni en durée, ni en intensité, sur l'ensemble de la période étudiée. Une étude statistique, confirmée par des représentations cartographiques de ces différentes périodes, met en évidence le caractère fortement hétérogène du phénomène dans l'espace. Cette diminution de la pluviométrie a de sérieuses conséquences sur les régimes d'écoulement des cours d'eau de ces régions. Cette étude a permis de caractériser ces modifications et d'apporter une dimension régionale à leur interprétation tout en soulignant la diminution importante des volumes écoulés ce qui n'est pas sans conséquences tant au niveau économique qu'environnemental

XAB2 promotes Ku eviction from single-ended DNA double-strand breaks independently of the ATM kinase

Replication-associated single-ended DNA double-strand breaks (seDSBs) are repaired predominantly through RAD51-mediated homologous recombination (HR). Removal of the non-homologous end-joining (NHEJ) factor Ku from resected seDSB ends is crucial for HR. The coordinated actions of MRE11-CtIP nuclease activities orchestrated by ATM define one pathway for Ku eviction. Here, we identify the pre-mRNA splicing protein XAB2 as a factor required for resistance to seDSBs induced by the chemotherapeutic alkylator temozolomide. Moreover, we show that XAB2 prevents Ku retention and abortive HR at seDSBs induced by temozolomide and camptothecin, via a pathway that operates in parallel to the ATM-CtIP-MRE11 axis. Although XAB2 depletion preserved RAD51 focus formation, the resulting RAD51-ssDNA associations were unproductive, leading to increased NHEJ engagement in S/G2 and genetic instability. Overexpression of RAD51 or RAD52 rescued the XAB2 defects and XAB2 loss was synthetically lethal with RAD52 inhibition, providing potential perspectives in cancer therapy.publishedVersio

Cyclodipeptide synthases, a family of class-I aminoacyl-tRNA synthetase-like enzymes involved in non-ribosomal peptide synthesis

Cyclodipeptide synthases (CDPSs) belong to a newly defined family of enzymes that use aminoacyl-tRNAs (aa-tRNAs) as substrates to synthesize the two peptide bonds of various cyclodipeptides, which are the precursors of many natural products with noteworthy biological activities. Here, we describe the crystal structure of AlbC, a CDPS from Streptomyces noursei. The AlbC structure consists of a monomer containing a Rossmann-fold domain. Strikingly, it is highly similar to the catalytic domain of class-I aminoacyl-tRNA synthetases (aaRSs), especially class-Ic TyrRSs and TrpRSs. AlbC contains a deep pocket, highly conserved among CDPSs. Site-directed mutagenesis studies indicate that this pocket accommodates the aminoacyl moiety of the aa-tRNA substrate in a way similar to that used by TyrRSs to recognize their tyrosine substrates. These studies also suggest that the tRNA moiety of the aa-tRNA interacts with AlbC via at least one patch of basic residues, which is conserved among CDPSs but not present in class-Ic aaRSs. AlbC catalyses its two-substrate reaction via a ping-pong mechanism with a covalent intermediate in which l-Phe is shown to be transferred from Phe-tRNAPhe to an active serine. These findings provide insight into the molecular bases of the interactions between CDPSs and their aa-tRNAs substrates, and the catalytic mechanism used by CDPSs to achieve the non-ribosomal synthesis of cyclodipeptides

Cooperation of breast cancer proteins PALB2 and piccolo BRCA2 in stimulating homologous recombination.

Inherited mutations in human PALB2 are associated with a predisposition to breast and pancreatic cancers. PALB2's tumor-suppressing effect is thought to be based on its ability to facilitate BRCA2's function in homologous recombination. However, the biochemical properties of PALB2 are unknown. Here we show that human PALB2 binds DNA, preferentially D-loop structures, and directly interacts with the RAD51 recombinase to stimulate strand invasion, a vital step of homologous recombination. This stimulation occurs through reinforcing biochemical mechanisms, as PALB2 alleviates inhibition by RPA and stabilizes the RAD51 filament. Moreover, PALB2 can function synergistically with a BRCA2 chimera (termed piccolo, or piBRCA2) to further promote strand invasion. Finally, we show that PALB2-deficient cells are sensitive to PARP inhibitors. Our studies provide the first biochemical insights into PALB2's function with piBRCA2 as a mediator of homologous recombination in DNA double-strand break repair

Belief Functions: Theory and Applications - Proceedings of the 2nd International Conference on Belief Functions

The theory of belief functions, also known as evidence theory or Dempster-Shafer theory, was first introduced by Arthur P. Dempster in the context of statistical inference, and was later developed by Glenn Shafer as a general framework for modeling epistemic uncertainty. These early contributions have been the starting points of many important developments, including the Transferable Belief Model and the Theory of Hints. The theory of belief functions is now well established as a general framework for reasoning with uncertainty, and has well understood connections to other frameworks such as probability, possibility and imprecise probability theories.   This volume contains the proceedings of the 2nd International Conference on Belief Functions that was held in Compiègne, France on 9-11 May 2012. It gathers 51 contributions describing recent developments both on theoretical issues (including approximation methods, combination rules, continuous belief functions, graphical models and independence concepts) and applications in various areas including classification, image processing, statistics and intelligent vehicles.